Practice Projectile

ABSTRACT

A practice mortar bomb comprising a pressure vessel and an outlet valve system, the pressure vessel being arranged in use to contain compressed fluid and the outlet valve system being arranged in use to allow explosive release of the compressed fluid from the pressure vessel upon activation of the valve system by a firing pin in a mortar tube.

FIELD OF INVENTION

The present invention relates to practice ammunition rounds. More specifically the invention relates to practice mortar bombs, a method of explosively releasing compressed fluid from a pressure vessel via an outlet valve system, a method of firing a practice mortar bomb, a method of propelling a practice mortar bomb and a kit of parts.

BACKGROUND OF THE INVENTION

A mortar is a weapon system typically used by infantrymen to provide indirect fire. Mortars are based around a mortar tube (the orientation of which is adjustable for aiming) down which is dropped a mortar bomb. Mortar bombs have a tail portion containing explosive propellant which is initiated by a firing pin at the bottom of the mortar tube. The resulting explosion combined with the tight fit of the bomb within the tube propels the bomb from the mortar barrel.

As will be appreciated it is highly desirable that operators should be given the opportunity of practicing with mortars before they are called upon to use them in combat. There are many skills to learn, including transporting, assembling, aiming and firing the mortar. Beyond this there are more specialised proficiencies such as firing patterns and use of different bomb types (e.g. smoke, illumination and high explosive).

In practicing these skills it is in many cases desirable to actually fire the weapon or at least to re-create actual firing of the weapon as accurately as possible. As will be appreciated there are however several draw-backs to practicing with a real mortar and live ammunition. A live mortar bomb is very expensive and is not re-usable. Firing live rounds also requires a large area (which may be quickly damaged if sufficient practice is undertaken). Further the use of live ammunition gives rise to the need for a great deal of attention to be given to safety, not only in use but also in procurement, storage and transport. This is time consuming and expensive.

As a consequence of the above it is normal for mortar teams to have very limited practice using live ammunition. In substituting for this it is known to practice by ‘going through the motions’ without actually firing a round. This is very limited in terms of the experience that it can provide and further is often considered boring and ineffective by mortar teams. Computer simulations are also used which can provide a more useful substitute for certain aspects such as aiming. Nonetheless there is still a need for a cheaper, safer method of more realistically practicing firing a mortar.

SUMMARY OF THE INVENTION

According to a first aspect of the invention a practice mortar bomb is provided comprising optionally a pressure vessel and optionally an outlet valve system, the pressure vessel being arranged in use to optionally contain compressed fluid and the outlet valve system being arranged in use to optionally allow explosive release of the compressed fluid from the pressure vessel optionally upon activation of the valve system by a firing pin in a mortar tube. This practice mortar bomb may provide a relatively safe, inexpensive and yet realistic way of practicing the firing of a mortar.

In some embodiments the practice mortar bomb further comprises an inlet valve system arranged in use to allow charging of the pressure vessel with fluid such that the fluid is compressed within the pressure vessel. The inlet valve system may provide a convenient way of filling the pressure vessel and may also allow re-use of the mortar bomb by re-filling the pressure vessel via the inlet valve system. This may make repeated practice considerably less expensive.

In some embodiments the inlet valve system comprises a one-way valve allowing storage of the compressed fluid in the pressure vessel once charged. The one-way valve may offer a convenient way of allowing filling of the pressure vessel and the retention of compressed fluid for an extended period thereafter.

In some embodiments the inlet valve system is positioned at a head end of the pressure vessel. Positioning of the inlet valve system in this way may allow for a reduced impact on the appearance and performance of the practice mortar bomb so as it better resembles a standard mortar bomb in appearance and performance.

In some embodiments the outlet valve system is positioned at a base end of the pressure vessel. This may lead to a more direct release of compressed fluid in the desired direction for firing of the bomb.

In some embodiments the outlet valve mechanism comprises a valve seat and valve body, the valve body being mobile such that in use a valve seat end of the valve body is engageable with the valve seat to block the flow of fluid from the pressure vessel, and is disengageable from the valve seat to allow the flow of fluid from the pressure vessel.

In some embodiments the outlet valve system is a pressure balance valve, being arranged such that in use, compressed fluid from the interior of the pressure vessel impinges on at least two opposed surfaces of the valve body, the resulting net force being towards the valve seat until the outlet valve system is activated, whereupon the net force is away from the valve seat. The pressure balance valve may be a particularly effective way of allowing explosive release of compressed fluid, as the compressed fluid itself may be used to move the valve body away from the valve seat and so open the outlet valve system. This may lead to a very rapid opening of the outlet valve system. Further the pressure balance valve may allow re-setting of the outlet valve system after explosive fluid discharge.

In some embodiments a first of the opposed surfaces is a head end of the valve body and a second of the opposed surfaces, opposed to the first is a biasing surface proximate the valve seat end of the valve body.

In some embodiments the outlet valve system further comprises a chamber arranged such that in use, compressed fluid in the chamber impinges on the head end of the valve body with sufficient force to cause engagement of the valve seat end of the valve body with the valve seat. The chamber may provide a convenient method of allowing compressed fluid to impinge on the head end, while also isolating (at least to an extent) the fluid in the chamber from fluid in the pressure vessel. This may mean that through discharging the chamber, at least some of the force biasing the valve body towards the valve seat may be removed.

In some embodiments the practice mortar bomb is arranged such that in use, activation of the outlet valve system leads to the release of compressed fluid from the chamber at a faster rate than it is replenished, such that the force biasing the valve body towards the valve seat is reduced and the net force on the valve body is reversed so as it is away from the valve seat. This may allow for rapid opening of the outlet valve system to permit explosive release of compressed fluid from the pressure vessel.

In some embodiments release of the compressed fluid from the chamber is controlled by a firing valve, operated in use directly or indirectly by a firing pin in a mortar tube. This may allow the firing pin in a standard mortar tube to initiate firing of the practice mortar bomb. In this way a specialist mortar tube may not be required, potentially increasing the realism of practice.

In some embodiments the outlet valve system is arranged such that in use it re-sets before all of the compressed fluid has been explosively released from the pressure vessel. In this way a positive pressure may be maintained in the pressure vessel, helping to prevent the ingress of foreign material such as dust, sand and/or water into the practice mortar bomb. This may be particularly advantageous in view of the fact that the practice mortar bomb may dig into the earth on landing (at least to an extent).

In some embodiments the outlet valve mechanism further comprises a cylinder in which the valve body moves and is contained in a close fit. The cylinder may be an effective way of guiding movement of the valve body and of creating the chamber adjacent the head end of the valve body.

In some embodiments the chamber is defined by the cylinder and the head end of the valve body.

In some embodiments the cylinder has one or more cylinder through bores arranged so that the interior of the pressure vessel is in fluid communication with the chamber, such that in use pressurised fluid passes from the pressure vessel into the chamber. The cylinder through bores may therefore allow charging of the chamber from compressed fluid in the pressure vessel, in order that the valve body may be biased towards the valve seat.

In some embodiments a region proximate the valve seat end of the valve body is provided with one or more rebated portions, each creating a cavity between the cylinder and the valve body. The cavities may assist in creating one or more surfaces for implementation of the pressure balance valve.

In some embodiments the rebated portions create the biasing surface of the valve body, arranged such that at least a component of a force applied towards the biasing surface would act to bias the valve body away from the valve seat.

In some embodiments the rebated portions comprise chamfering of the valve seat end of the valve body that extends beyond the valve seat and into the cylinder when the valve seat end of the valve body is engaged with the valve seat. The chamfering may assist in locating of the valve seat end of the valve body within the valve seat, and it may conveniently also provide the biasing surface.

In some embodiments one or more passages is provided passing through the cylinder wall allowing fluid communication between the interior of the pressure vessel and the cavities. This may allow fluid pressure to be applied to the biasing surfaces from the pressure vessel for implementing the fluid balance valve.

In some embodiments fluid gaps are provided intermediate the passages and cavities, created by an increase in the diameter of the cylinder between the passages and the cavities. Where these fluid gaps have a relatively narrow diameter in comparison to the passages, the fluid gaps may be sufficient to cause the valve body to rapidly disengage the valve seat. Thereafter as the valve body clears the passages fluid may be explosively released via the passages which may be of a relatively large diameter.

In some embodiments the head end of the valve body has a sufficient surface area such that if the same pressure were applied to the head end of the valve body and the biasing surface, the net force on the valve body would cause the valve seat end of the valve body to engage with the valve seat. This may ensure that the default condition of the outlet valve system is closed so as to prevent discharge of fluid from the pressure vessel until compressed fluid is discharged from the chamber.

In some embodiments the valve body has a valve body through bore passing from the head end of the valve body to the valve seat end of the valve body. This may provide a convenient path for discharging compressed fluid from the chamber when the outlet valve system is activated.

In some embodiments the head end of the valve body through bore is provided with a firing valve seat.

In some embodiments a firing valve body is provided which, when there is compressed fluid in the chamber, is biased by the compressed fluid into engagement with the firing valve seat. This may ensure that the default condition of the firing valve is closed, preventing the discharge of fluid from the chamber (and so the opening of the outlet valve system) until the valve is activated.

As will be appreciated in some embodiments a spring may be provided to increase the force biasing the firing valve body into engagement with the valve seat.

In some embodiments a pin of smaller diameter than the valve body through bore extends from the firing valve body through the valve body through bore. This pin may provide a convenient method of activating the outlet valve system, in that pushing on the pin may open the firing valve, by raising the firing valve body from the firing valve seat.

In some embodiments the pin is arranged to force the firing valve away from the firing valve seat when an end of the pin is impacted by a firing pin in a mortar tube. The pin may therefore act as an intermediary between the firing pin of the mortar tube and the firing valve body. It this way it may be possible to use a conventional mortar tube.

In some embodiments the cylinder through bore and valve body through bore are arranged such that greater quantities of fluid at a given pressure are passable through the valve body through bore than through the cylinder through bore in a given time. This may ensure that for as long as the firing pin of the mortar tube is keeping the firing valve open, the chamber cannot re-charge with pressurised fluid. This may mean that the outlet valve system will open and remain open, at least until the bomb is fired.

In some embodiments the practice mortar bomb further comprises a dummy fuse nose portion. The nose portion may mean that the practice mortar bomb is more like a standard mortar bomb, i.e. in terms of appearance and/or aerodynamic profile and/or shape and/or size and/or weight, thus potentially making its use in practice more realistic.

In some embodiments the nose portion simulates a known mortar bomb fuse type. This may make the practice mortar bomb more like a standard mortar bomb, i.e. in terms of appearance and/or aerodynamic profile and/or shape and/or size and/or weight, thus potentially making its use in practice more realistic. The fuse may for example simulate a point detonation fuse, a proximity fuse, a mechanical time fuse, a multi-option fuse or a practice fuse.

In some embodiments the nose portion is releasably engageable with the bomb. This may allow the nose portion to be interchangeable with alternatives simulating different dummy fuses, depending on the practice to be undertaken.

In some embodiments the nose portion provides a cap over the inlet valve system. This may serve to protect the nose portion especially during impact of the practice mortar bomb on landing.

In some embodiments the bomb further comprises a hollow tail portion, the interior of the tail portion being in fluid communication with the pressure vessel when the outlet valve system is open. The tail portion may allow more accurate simulation of the appearance of a standard mortar bomb. Further the tail portion may receive the explosively released fluid from the outlet valve system, allowing it to be directed.

In some embodiments the tail portion comprises one or more ports allowing fluid communication between its interior and exterior. The ports may be used to direct explosively released fluid into a mortar tube below the level of the pressure vessel.

In some embodiments the tail portion has a tail portion through bore arranged in use to receive at least one of the pin and, in use the firing pin of a mortar tube. The tail portion through bore may help to ensure that the firing pin of the mortar tube is properly aligned and received by the practice mortar bomb in order that it may displace the pin.

In some embodiments the pin is of sufficient length and aligned with the tail portion through bore so as a firing pin of a mortar entering the tail portion through bore will impact and push against the pin so as to push the firing valve body away from the firing valve seat. This may help to ensure a proper contact between the pin and firing pin of a mortar tube.

In some embodiments the practice mortar bomb has an overfill pressure release valve. This may be an effective safety feature against over charging of the pressure vessel.

According to a second aspect of the invention there is provided a kit of parts comprising optionally one or more pressure vessels for practice mortar bombs in accordance with the first aspect and optionally one or more of the following:

-   -   one or more nose portions optionally of various designs to         simulate different known mortar bomb fuse types,     -   one or more tail portions,     -   one or more pumps.         Such kits may be convenient especially when practice is being         undertaken. For example a mortar team may select different fuses         when practicing different fire missions and may re-charge the         pressure vessel on the practice range using the pump.

According to a third aspect of the invention a method of explosively releasing compressed fluid from a pressure vessel via an outlet valve system is provided, the pressure vessel and outlet valve system being provided in a practice mortar bomb, comprising the steps of:

-   -   exposing a valve body of the valve system to pressure from the         compressed fluid acting in at least two different locations so         as to bias the valve body both towards and away from a valve         seat, with the net force being towards the valve seat,     -   activating the valve to release compressed fluid from at least         one of the location to reduce the force acting to bias the valve         body towards the valve seat so that the net force is away from         the valve seat.         This method may allow rapid release of the compressed fluid in a         manner sufficient to propel the practice mortar bomb a desired         distance.

In some embodiments the method further comprises re-charging the location from which compressed fluid has been released so as the net force is again towards the valve seat. This may allow the practice mortar bomb to be re-used by re-charging the pressure vessel.

According to a fourth aspect of the invention a method of firing a practice mortar bomb is provided, the practice mortar bomb comprising optionally a pressure vessel and optionally an outlet valve system optionally arranged upon activation to explosively release at least a portion of a compressed air reservoir in the pressure vessel, the method comprising the steps of:

-   -   optionally charging the pressure vessel with compressed fluid,         and     -   optionally dropping the mortar bomb down a mortar tube.         This method may be more realistic for those practicing the skill         of mortaring than going through the motions without actually         firing a mortar bomb. Further the method may be safer and         relatively inexpensive in comparison to using a real mortar         bomb.

In some embodiments the method further comprises collecting the practice mortar bomb for optional re-use. This may improve cost effectiveness of mortar practice.

In some embodiment the method further comprises selecting a head portion for attachment to the practice mortar bomb before it is fired. This may allow a mortar user to more accurately simulate performing different fire missions by selecting different dummy fuse head portions.

According to a fifth aspect of the invention a method of propelling a practice mortar bomb is provided comprising explosively releasing compressed fluid contained within the practice mortar bomb via an outlet valve system. This system may eliminate the need for using an explosive charge (which may be more expensive and dangerous) during practicing the skill of mortaring.

The skilled person will appreciate that a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention.

BRIEF DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying Figures, in which:

FIG. 1 is a cut-away view showing a practice mortar bomb in accordance with an embodiment of the invention;

FIG. 2 is an enlargement of part A of FIG. 1 showing a cross-section of an outlet valve system according to an embodiment of the invention;

FIG. 3 is a cut-away view showing an alternative practice mortar bomb in accordance with an embodiment of the invention;

FIG. 4 is an enlargement of part A of FIG. 3 showing a cross-section of an outlet valve system according to an embodiment of the invention;

FIG. 5 is a cut-away view showing an alternative practice mortar bomb in accordance with an embodiment of the invention; and

FIG. 6 is an enlargement of part A of FIG. 5 showing a cross-section of an outlet valve system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring first to FIG. 1 a practice mortar bomb is generally provided at 100. Such a practice mortar may be provided in various calibres to facilitate firing from standard mortar tubes (e.g. 51, 60, 81 or 120 mm). The practice mortar bomb 100 is 60 mm, but as will be appreciated this is not intended to be limiting.

The bomb 100 comprises a main body portion 104 positioned intermediate a nose portion 102 and a tail portion 106.

The main body portion 104 is substantially ellipsoid in shape and is provided by head element 108 and base element 110. The head and base elements 108, 110 are releasably engageable using cooperating main body screw threaded regions 112. The base element is provided with an annular rebate 114 on its exterior surface which may be used to receive an obturating ring (not shown).

The main body portion 104 defines a pressure vessel 116 in the form of a void surrounded by the main body portion 104 walls.

At a head end of the pressure vessel 116 the head element 108 is shaped to provide an inlet valve system housing 118 in the form of a cylindrical portion, coaxial with the main body 104 and having a reduced diameter. In the inlet valve system housing 118 is positioned an inlet valve system (not shown here for clarity) comprising a one way valve allowing charging of the pressure vessel 116.

At a base end of the pressure vessel 116 the base element 110 is shaped to provide a valve seat 120 for an outlet valve system 122 (described in greater detail later with reference to FIG. 2).

The nose portion 102 (which in some embodiments may be a dummy fuse) is substantially conical in shape and has a hollow interior portion 124 to accommodate protruding portions of the inlet valve system. The nose portion 102 is releasably engageable with the head element 108 using cooperating nose screw threaded regions 126.

The tail portion 106 is substantially cylindrical in shape and has a hollow interior portion 128 in fluid communication with the valve seat 120. The tail portion 106 is provided with a plurality of ports 130 through its sidewall 132, the ports 130 providing fluid communication between the hollow interior portion 128 and the exterior of the tail portion 106. The tail portion further comprises a plurality of stabilising fins 134 projecting outwards from the tail portion 106. The tail portion 106 has a tail portion through bore 136 which receives a pin 138 passing from the outlet valve system 122, through the hollow interior portion 128 and through the tail portion through bore 136. The tail portion 106 is releasably engageable with the base element 110 using cooperating tail screw threaded regions 140.

Referring now to FIG. 2 the parts of the outlet valve system 122 are described. The outlet valve system 122 has a valve body 142 engageable with the valve seat 120. In FIG. 2 the valve body 142 is shown in an engaged position with the valve seat 120. It will be appreciated however that the valve body 142 is mobile and consequently may also be disengaged from the valve seat 120 by raising the valve body 142.

The valve body 142 is substantially cylindrical and has a head end 144 and a valve seat end 146.

The head end 144 is provided with a firing valve seat 148 comprising a countersunk region of a valve body through bore 150 which passes through the valve body 142 from the head end 144 to the valve seat end 146. Engaged with the firing valve seat 148 is a firing valve body 152. In FIG. 2 the firing valve body 152 is shown in an engaged position with the firing valve seat 148. It will be appreciated however that the firing valve body 152 is mobile and consequently may also be disengaged from the firing valve seat 148 by raising the firing valve body 152. Extending from the firing valve body 152, through the valve body through bore 150 is the pin 138. The pin 138 has a smaller diameter than the valve body through bore 150. The pin 138 is guided and supported proximate the valve seat end 146 by a pin guide plate 154.

The valve seat end 146 has a chamfered peripheral (and is therefore rebated) that extends beyond the valve seat and into a cylinder 156 when the valve seat end 146 is engaged with the valve seat 120. The chamfering provides a biasing surface 158 opposed to the head end 144 of the valve body 142.

The cylinder 156 surrounds the valve body 142 in a close fit, supporting movement of the valve body 142. The cylinder and the head end 144 define a chamber 160. The chamber 160 is in fluid communication with the pressure vessel 116 via a cylinder through bore 162.

The cylinder 156 and biasing surface 158 define a cavity 164. As a consequence of fluid gaps 165 and passages 166, the cavity 164 is in fluid communication with the interior of the pressure vessel 116. The passages 166, which pass through the cylinder 156, are further defined by the cylinder 156 and base element 110 walls. The fluid gaps 165 have a total cross-sectional area that is considerably less than the total cross-sectional area of the passages 166. The fluid gaps 165 are formed by an increase in the diameter of the cylinder 156, between the passages 166 and the cavity 164.

In use the practice mortar bomb 100 may be used by someone wishing to practice the skill of firing a mortar and or associated skills. Exemplary use and operation of the practice mortar bomb 100 is now provided with reference to FIGS. 1 and 2.

The user first disengages the nose portion 102 using nose screw threaded regions 126, giving access to the inlet valve system. The user then charges the pressure vessel 116 with compressed fluid via the inlet valve system 116. This may for example be achieved via use of a pump or compressor. Any suitable compressed fluid may be used, for example air or nitrogen. The pressure vessel 116 is charged to a pressure in accordance with a desired range and the calibre of the practice mortar bomb. By way of example the pressure vessel of a 60 mm practice mortar bomb 100 might be charged to between 20 and 100 bar, preferably between 35 and 60 bar and more preferably to between 45 and 50 bar.

Compressed fluid in the pressure vessel 116 is free to pass into chamber 160, where it impinges on the head end 144 of the valve body 142 with sufficient force to engage the valve seat end 146 of the valve body 142 with the valve seat 120. This prevents the flow of compressed fluid from the pressure vessel 116 through the outlet valve system 122.

Compressed fluid in the pressure vessel 116 is also free to pass through passages 166 and fluid gaps 165 into cavities 164, where it impinges on the biasing surface 158. This pressure on the biasing surface 158 biases the valve seat end 146 to disengage from the valve seat 120. However the net force on the valve body 142 is such that the valve seat end 146 remains engaged with the valve seat 120. This is due to the relative surface areas of the opposed surfaces (the head end 144 and biasing surface 158).

Compressed fluid in the chamber 160 also impinges on the firing valve body 152 forcing it to engage the firing valve seat 148. This prevents compressed fluid being discharged from the chamber 160 via the valve body through bore 150.

The user then selects a nose portion 102 corresponding to the appearance of a particular fuse type, (e.g. detonation fuse, proximity fuse, a mechanical time fuse, a multi-option fuse or a practice fuse) corresponding to a simulated fire mission to be undertaken. The selected nose portion 102 is then engaged using the nose screw threaded regions 126.

The user then drops the practice mortar bomb 100 down a mortar tube (not shown) in which the practice mortar bomb 100 is a tight fit. When the practice mortar bomb 100 reaches the bottom of the mortar tube it engages a firing pin in the bottom of the tube. The firing pin is received in the tail portion through bore 136 and displaces the pin 138 upwards. The pin 138, guided and supported by the tail portion through bore 136 and pin guide plate 154, disengages the firing valve body 152 from the firing valve seat 148, moving it upwards. This allows compressed fluid in the chamber 160 to rapidly discharge from the chamber 160 via the fluid body through bore 136, hollow interior portion 128 and plurality of ports 130. Further due to the relative diameters of the cylinder through bore 162 (smaller) and fluid body through bore 136 (larger), the cavity 160 cannot be re-pressurised while the firing valve body 152 is disengaged from the firing valve seat 148.

The practice mortar bomb 100 is also suitable for use in mortar tubes that have an externally triggerable firing pin which is activated after the practice mortar bomb 100 has been inserted into the tube.

As a consequence of the drop in pressure in the chamber 160, compressed fluid impinging on the biasing surface 158 causes a reversal in the net force on the valve body 142, forcing the valve body 142 upwards so as the valve seat end 146 disengages with the valve seat 120. As the valve body 142 moves upwards the valve seat end 146 passes the passages 166, which due to their large diameter allow rapid discharge of the compressed fluid from the pressure vessel 116 via the hollow interior portion 128 and plurality of ports 130. This explosive release of compressed fluid rapidly fills the area of the mortar tube between the practice mortar bomb and the tube. Due to the tight fit of the practice mortar bomb 100 within the mortar tube, and action of an obturating ring (not shown) to create an enhanced seal, the released compressed air propels the practice mortar bomb 100 from the mortar tube.

As the practice mortar bomb 100 is fired the firing pin in the mortar tube is removed from the tail portion through bore 136. This leaves the pin 138 free to return to its original position and the firing valve body 144 to engage with the firing valve seat 148 under the influence of remaining compressed gas in the chamber 160. In this condition the chamber 160 is allowed to re-pressurise via the cylinder through bore 162 and the valve body 142 is forced to engage the valve seat 120. This ensures that as the practice mortar bomb 100 is fired, compressed fluid remaining in the pressure vessel 116 is retained, meaning that a positive pressure is maintained within the pressure vessel 116. This may help to prevent the ingress of foreign material into the practice mortar bomb 100. Further it means that the valve is re-set and ready for re-use of the practice mortar bomb.

In view of the influence on the position of the valve body 142 exerted by the compressed fluid acting on the opposed surfaces (head end 144 and biasing surface 158) the outlet valve system 122 may be referred to as a pressure balance valve. Further the opposed surfaces may be considered to be locations on which pressure from the compressed fluid may act.

Referring now to FIGS. 3 and 4 an alternative practice mortar bomb is generally provided at 200. The practice mortar bomb 200 is similar to the practice mortar bomb 100 except that an alternative outlet valve system 222 is provided.

The outlet valve system 222 is similar to the outlet valve system 122, but several modifications have been made.

The outlet valve system 222 has a valve body 242 engageable with the valve seat 220. In FIG. 4 the valve body 242 is shown in an engaged position with the valve seat 220. It will be appreciated however that the valve body 242 is mobile and consequently may also be disengaged from the valve seat 220 by raising the valve body 242.

The valve body 242 is substantially cylindrical and has a head end 244 and a valve seat end 246.

The head end 244 is provided with a firing valve seat 248 comprising a countersunk region of a valve body through bore 250, passing through the valve body 242 from the head end 244 to the valve seat end 246. Engaged with the firing valve seat 248 is a firing valve body 252. In FIG. 4 the firing valve body 252 is shown in an engaged position with the firing valve seat 248. It will be appreciated however that the firing valve body 252 is mobile and consequently may also be disengaged from the firing valve seat 248 by raising the firing valve body 252. Extending from the firing valve body 252, through the valve body through bore 250 is a pin 238. The pin 238 has a smaller diameter than the valve body through bore 250. The pin 238 is guided and supported proximate the valve seat end 246 by a pin guide plate 254.

The valve seat end 246 has a chamfered peripheral and a rebated portion 255 formed by a reduction in the diameter of the valve body 242. The rebated portion 255 provides a biasing surface 258 opposed to the head end 244 of the valve body 242.

A cylinder 256 surrounds the valve body 242 in a close fit, supporting movement of the valve body 242. The cylinder and the head end 244 define a chamber 260 and a spring guide 261. The chamber 260 is in fluid communication with the pressure vessel 216 via a cylinder through bore 262 and a flat 262 a in the firing valve body 252. A spring 263 provided within the spring guide is in contact with the firing valve body 252 and biases it towards the firing valve seat 248.

The cylinder 256 and biasing surface 258 define a cavity 264. As a consequence of passages 266, the cavity 264 is in fluid communication with the interior of the pressure vessel 216. The passages 266, which pass through the cylinder 256, are further defined by the cylinder 256 and base element 210 walls.

In the embodiment of FIGS. 3 and 4 the spring 263 helps to prevent leakage of fluid through the valve body through bore 250 before firing of the practice mortar bomb. The spring also assists with re-engaging the firing valve body 252 with the firing valve seat 248 once explosive release of compressed fluid has occurred, in order that the outlet valve system 222 is re-set and a positive pressure is maintained in the pressure vessel 216. Further the arrangement of the rebated portion 255, which increases the size of the cavity 264, means that compressed fluid may be released more quickly than with the arrangement of FIG. 2.

Referring now to FIGS. 5 and 6 an alternative practice mortar bomb is generally provided at 300. The practice mortar bomb 300 is similar to the practice mortar bomb 200 except that for a number of features.

The exterior wall of a spring guide 361 is provided with a spanner/wrench formation 370 (in this case hexagonal) to facilitate screwing and unscrewing of a cylinder 356 to a base element 310 during assembly/disassembly of the practice mortar bomb 300.

A further modification of the practice mortar bomb 300 is that a valve body 342 is provided with a seal 372 (in this case an O-ring) to improve the seal between the valve body 342 and the cylinder 356. Further a countersunk region of a valve body through bore 350 is curved so as a firing valve seat 348 in a head end 344 of the valve body 342 cooperates in a close fit with a curved engagement surface 374 of a firing valve body 352. This curved arrangement (which may be hemispherical) improved seating of the firing valve body.

It will be further noted that in the FIGS. 5 and 6 embodiments no pin guide plate is provided, which highlights that this feature is optional.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the various concepts described herein. Any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and sub-combinations of one or more features described herein in any form of practice mortar bomb. 

1. A practice mortar bomb comprising a pressure vessel and an outlet valve system, the pressure vessel being arranged in use to contain compressed fluid and the outlet valve system being arranged in use to allow explosive release of the compressed fluid from the pressure vessel upon activation of the valve system by a firing pin in a mortar tube.
 2. A practice mortar bomb according to claim 1, further comprising an inlet valve system arranged in use to allow charging of the pressure vessel with fluid such that the fluid is compressed within the pressure vessel.
 3. A practice mortar bomb according to claim 1, where the outlet valve mechanism comprises a valve seat and valve body, the valve body being mobile such that in use a valve seat end of the valve body is engageable with the valve seat to block the flow of fluid from the pressure vessel, and is disengageable from the valve seat to allow the flow of fluid from the pressure vessel.
 4. A practice mortar bomb according to claim 3, where the outlet valve system is a pressure balance valve, arranged such that in use, compressed fluid from the interior of the pressure vessel impinges on at least two opposed surfaces of the valve body, the resulting net force being towards the valve seat until the outlet valve system is activated, whereupon the net force is away from the valve seat.
 5. A practice mortar bomb according to claim 4, where the outlet valve system further comprises a chamber arranged such that in use, compressed fluid in the chamber impinges on a head end of the valve body with sufficient force to cause engagement of the valve seat end of the valve body with the valve seat.
 6. A practice mortar bomb according to claim 5, arranged such that in use, activation of the outlet valve system leads to the release of compressed fluid from the chamber at a faster rate than it is replenished, such that the force biasing the valve body towards the valve seat is reduced and the net force on the valve body is reversed so as it is away from the valve seat.
 7. A practice mortar bomb according to claim 6, where release of the compressed fluid from the chamber is controlled by a firing valve, operated in use directly or indirectly by a firing pin in a mortar tube.
 8. A practice mortar bomb according to claim 5, where the outlet valve mechanism further comprises a cylinder and wherein the chamber is defined by the cylinder and the head end of the valve body.
 9. A practice mortar bomb according to claim 8, where the cylinder has at least one cylinder through bore arranged so that the interior of the pressure vessel is in fluid communication with the chamber, such that in use pressurised fluid passes from the pressure vessel into the chamber.
 10. A practice mortar bomb according to claim 3, where a region proximate the valve seat end of the valve body is provided with at least one rebated portion, where each rebated portion creates a cavity between the cylinder and the valve body.
 11. A practice mortar bomb according to claim 10, where the at least one rebate portion creates at least one biasing surface of the valve body, arranged such that at least a component of a force applied towards the biasing surface would act to bias the valve body away from the valve seat.
 12. A practice mortar bomb according to claim 3, where the valve body has a valve body through bore passing from the head end of the valve body to the valve seat end of the valve body.
 13. A practice mortar bomb according to claim 12, where the head end of the valve body through bore is provided with a firing valve seat.
 14. A practice mortar bomb according to claim 13, where a firing valve body is provided which, when there is compressed fluid in the chamber, is biased by the compressed fluid into engagement with the firing valve seat.
 15. A practice mortar bomb according to claim 12, where a pin of smaller diameter than the valve body through bore extends from the firing valve body through the valve body through bore.
 16. A practice mortar bomb according to claim 15, where the pin is arranged to force the firing valve away from the firing valve seat when an end of the pin is impacted by a firing pin in a mortar tube.
 17. A practice mortar bomb according to claim 1, where the bomb further comprises a hollow tail portion, the interior of the tail portion being in fluid communication with the pressure vessel when the outlet valve system is open.
 18. A practice mortar bomb according to claim 17, where the tail portion comprises at least one port allowing fluid communication between its interior and exterior.
 19. A practice mortar bomb according to claim 17, where the tail portion has a tail portion through bore arranged in use to receive at least one of the pin and, in use the firing pin of a mortar tube.
 20. A kit of parts comprising one or more pressure vessels for practice mortar bombs in accordance with claim 1 and one or more of the following: one or more nose portions of various designs to simulate different known mortar bomb fuse types, one or more tail portions, one or more pumps.
 21. A method of firing a practice mortar bomb, the practice mortar bomb comprising a pressure vessel and an outlet valve system arranged upon activation to explosively release at least a portion of a compressed air reservoir in the pressure vessel, the method comprising the steps of: charging the pressure vessel with compressed fluid, and dropping the mortar bomb down a mortar tube. 